Free‐Fixed Rotational Triboelectric Nanogenerator for Self‐Powered Real‐Time Wheel Monitoring

Abstract

Transportation has always been necessary for propelling the development of human civilization.[1,2] For example, railway networks save much time and bring immeasurable economic benefits.[3] As a common sense, safety is a precondition for railway operation. Consequently, as a crucial and wear-prone component, wheel attracts considerable attention due to its health and stability monitoring.[4–6] However, the sensors for detection are usually powered by traditional cables, requiring wear-proof collecting rings with complex wire management. On the other hand, although energy storage devices including batteries and supercapacitors have a rapid development these years,[7–11] they constantly need to be replaced and cause potential environment damage due to the toxic materials used in the fabrication process. As the world entering the era of internet of things (IoTs),[12–14] self-powered technology for sensors by harvesting environment energy is derived since the power needed to operate each sensor is small.[15–21] Self-powered technology by triboelectric nanogenerators (TENGs) shows great potential for distributed power sources with advantages of cost effective, light weight, and high conversion efficiency.[18,22–27] Moreover, large amounts of mechanical energy on wheels are proved to be harvested by TENGs, according to previous works.[28–30] Even so, the development of TENGs for train wheels is still hindered because of the special structure of train. Widely applied in many fields, TENG is highlighted for its variable structure in special application environment, such as medicine,[31,32] constructions,[33,34] blue energy,[35–37] and so on. In this regard, designing a new structure of TENG for acclimatization is highly desirable and mandatory. In this work, we proposed a free-fixed TENG (FF-TENG) with rotation mode for wheel train monitoring by fixing magnets on the stator and bogie. Thus, the stator is not fixed directly on the bogie, without a serious negative impact on the wheel. The magnetic force not only immobilizes the stator, but also increases the contact areas between the stator and rotator to improve output. With the rational structure design, FF-TENG delivers a short-circuit current of 55 μA, an open-circuit voltage Developing an applicable triboelectric nanogenerator (TENG) for train wheel energy harvesting is a key step to meet the urgent need of wheel safety monitoring. Herein, an innovative design of free-fixed TENG (FFTENG) is reported, without a serious negative impact on the wheel. The key of this design is the magnets fixed on the device and bogie, providing attractive force to immobilize the stator. With a rotational structure, FF-TENG can provide a high short-circuit current of 55 μA, an opencircuit voltage of 500 V, and a charge of 235 nC at a rotation speed of 400 rpm. At an external load resistance of 10 MΩ, FF-TENG delivers the maximum power of 15.68 mW. Furthermore, the superior robustness of FF-TENG in vibration environment is proved. In addition, a power management circuit designed by LTC 3588 is tested for more efficient capacitor charging, leading to better performance to power electronics. Finally, a self-powered real-time wheel temperature and wheel speed monitoring system is developed with FF-TENG as a safety alert demo for feasibility demonstration. Given the rational structure design and high performance, this work paves a practical way for TENGs in the field of intelligent transportation.